Method of and apparatus for washing photomask and washing solution for photomask

ABSTRACT

Organic matter and metal impurities present on the surface of a photomask are removed. Foreign matter still adhering to the surface of the photomask is removed with H 2  gas dissolved water. The photomask is dried. Thus provided is a method of washing a photomask in a manner which permits attaining an effect of removing foreign matter equivalent or superior to that of a conventional method with a small amount of chemical solution and reducing the amounts of chemicals and high purity water.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention generally relates to a method of washing aphotomask used as an original plate in a photolithography step forfabricating a semiconductor device (LSI), and more particularly, itrelates to an improved method of washing a photomask in an improvedmanner which permits obtaining a extremely dean surface. The presentinvention also relates to an apparatus for washing a photomask in animproved manner which permits obtaining a extremely clean surface. Thepresent invention further relates to a washing solution capable ofobtaining such a photomask having an extremely clean surface.

2. Description of the Prior Art

A photomask is used as an original plate when transferring the patternof an integrated circuit onto a surface of a wafer with a transfer unitin a photolithography step for fabricating a semiconductor device. Ifthe pattern formed on a surface of the photomask is defective or thephotomask is foul with foreign matter exceeding the resolution limit,the defect or the foreign matter is disadvantageously transferred ontothe wafer as part of the pattern. Therefore, no defect or foreign matterexceeding the resolution limit is allowed on the surface of thephotomask. Due to high integration and refinement of the integratedcircuit, the size of allowable defect or foreign matter is limited tonot more than 0.5 μm.

In general, such a photomask is washed by a method based on RCA washing,employing a mixed solution of acid such as sulfuric acid and aqueoushydrogen peroxide and a mixed solution of an alkaline chemical solutionsuch as aqueous ammonia and aqueous hydrogen peroxide, which has beenfield-proven in a wafer washing step.

FIG. 11 illustrates the flow of the conventional washing process.

In a step 1, the photomask is washed with a high-temperature mixedsolution of sulfuric acid and aqueous hydrogen peroxide, in order todecompose organic matter such as resist or a solvent present on thesurface of the photomask and remove metal impurities. The wettability ofthe mask surface is improved through this step to improve the efficiencyof later washing.

Then, in a step 2, the photomask is rinsed with high purity water forremoving chemicals such as sulfuric acid

Then, in a step 3, the photomask is dipped in a tank and washed in aheated mixed solution of ammonia and aqueous hydrogen peroxide, in orderto remove foreign matter adhering to the photomask. At this time,ultrasonic waves such as megasonic waves may be applied to the dippingtank.

Also after the step 3, the photomask must be sufficiently rinsed withhigh purity water in a step 4. Finally, the photomask rinsed with highpurity water is dried in a step 5. At the step 3, the photomask may bewashed not with the mixed solution of ammonia and aqueous hydrogenperoxide but with only high purity water or high purity water mixed witha detergent, with application of ultrasonic waves such as megasonicwaves.

In the aforementioned dipping system, the throughput can be improved bysimultaneously dipping a plurality of photomasks in one tank, while aremarkably contaminated photomask may disadvantageously contaminateother relatively clean photomasks.

In order to improve this point, a spin washing method of horizontallyrotating a photomask and applying a chemical solution, high purity wateror the like thereto from a fixed or swinging nozzle is performed as asystem throwing away the chemical solution for washing a singlephotomask. In the spin system, the photomask may be subjected tomechanical washing such as high-pressure high purity water jet rinsing,megasonic high purity water rinsing or the like for further effectivelyremoving foreign matter.

The aforementioned step 3 of treating the photomask with aqueousammonia/aqueous hydrogen peroxide for removing foreign matter has thefollowing problem: In the dip washing, a plurality of photomasks aretreated with the same chemical solution, and hence the chemical solutionmust be frequently renewed to avoid its deterioration or contamination,leading to increase of the amount of the chemical solution consumed. Ifthe washing efficiency (washing yield) is inferior, each photomask iswashed a plurality of times, to result in increase of the amounts ofchemicals or high purity water and energy such as electricity.

A phase-shift photomask improving the resolution of resist on a wafer bypartially shifting the phase of light transmitted through the photomaskhas recently been developed and put into practice. An MoSiON film isused as a material of a shading mask for a halftone photomask, which isa kind of such phase-shift photomask.

However, the transmittance and the phase angle of the MoSiON filmremarkably fluctuate through washing with an alkaline chemical such asthe conventional dipping in aqueous ammonia/aqueous hydrogen peroxide.Thus, the MoSiON film cannot keep its quality when the photomask isshipped as a product. Therefore, washing with aqueous ammonia/aqueoushydrogen peroxide effective for removing foreign matter cannot beapplied to the MoSiON film, which is in practice washed with only highpurity water or a detergent. Thus, foreign matter disadvantageouslyremains on the MoSiON film.

SUMMARY OF THE INVENTION

The present invention has been proposed in order to solve theaforementioned problem, and an object thereof is to provide a method ofwashing a photomask in an improved manner which permits attaining aneffect of removing foreign matter equivalent or superior to that of theconventional method with a small amount of chemical solution andreducing the amounts of chemicals and high purity water consumed.

Another object of the present invention is to provide a method ofwashing a photomask in an improved manner which permits effectivelyremoving foreign matter without changing the transmittance etc. of ashading film (MoSiON film) of a phase-shift photomask.

Still another object of the present invention is to provide a washingapparatus capable of implementing such a washing method.

A further object of the present invention is to provide a washingsolution for a photomask capable of implementing such a method ofwashing a photomask.

In a method of washing a photomask according to a first aspect of thepresent invention, organic matter and metal impurities present on asurface of a photomask are first removed. Foreign matter adhering to thesurface of the photomask is removed with H₂ gas dissolved water. Thephotomask is dried.

According to this method, the H₂ gas dissolved water is so employed asto remove the foreign matter at a high removal ratio.

In a method of washing a photomask according to a second aspect of thepresent invention, the H₂ gas dissolved water is alkalized. Thus, theforeign matter is removed at a higher removal ratio.

In a method of washing a photomask according to a third aspect of thepresent invention, the H₂ gas dissolved water is alkalized with ammonia.

According to this method, the H₂ gas dissolved water contains ammonia,whereby the foreign matter is removed at a higher removal ratio.

In a method of washing a photomask according to a fourth aspect of thepresent invention, the H₂ gas dissolved water is alkalized with a smallamount of KOH. Thus, the foreign matter is removed at a higher removalratio.

In a method of washing a photomask according to a fifth aspect of thepresent invention, ultrasonics waves are also employed in the step ofremoving foreign matter.

According to this method, that particulate foreign matter adhering tothe surface of the photomask can be effectively removed by alsoemploying ultrasonics waves.

In a method of washing a photomask according to a sixth aspect of thepresent invention, ultrasonics waves are also employed also in the firststep of removing organic matter and metal impurities. The organic matterand metal impurities are further efficiently removed due to theemployment of ultrasonics waves.

In a method of washing a photomask according to a seventh aspect of thepresent invention, the foreign matter is particulate foreign matter.Such particulate foreign matter can be readily physically removed byultrasonics waves.

An apparatus for washing a photomask according to an eighth aspect ofthe present invention comprises an acid tank for removing organic matterand metal impurities present on the surface of a photomask with a firstwashing solution. The washing apparatus also comprises a foreign matterremoving tank for removing foreign matter adhering to the surface of thephotomask with a second washing solution containing H₂ gas dissolvedwater. The washing apparatus further comprises a drying tank for dryingthe photomask. The washing apparatus further comprises a first washingsolution supply unit supplying the first washing solution to the acidtank and a second washing solution supply unit supplying the secondwashing solution to the foreign matter removing tank. The first washingsolution supply unit is provided with a first control unit forcontrolling the concentration and the temperature of the first washingsolution. The second washing solution supply unit is provided with asecond control unit controlling the concentration and the temperature ofthe second washing solution.

The foreign matter adhering to the surface of the photomask is removedwith the washing solution containing H₂ gas dissolved water.

Thus, the foreign matter can be removed from the mask at a high removalratio.

In an apparatus for washing a photomask according to a ninth aspect ofthe present invention, the foreign matter removing tank is provided witha ultrasonics unit giving off ultrasonic waves into the foreign matterremoving tank.

By use of this apparatus, the photomask can be treated with ultrasonicwaves, whereby particulate foreign matter can be effectively removed.

In an apparatus for washing a photomask according to a tenth aspect ofthe present invention, the acid tank is provided with a ultrasonics unitgiving off ultrasonic waves into the acid tank.

By use of this apparatus, ultrasonic waves are sent also into the acidtank, whereby the washing efficiency is improved.

In an apparatus for washing a photomask according to an eleventh aspectof the present invention, the foreign matter removing tank is furtherprovided with an aqueous ammonia supply unit supplying aqueous ammoniaof prescribed concentration into the foreign matter removing tank.

By use of this apparatus, ammonia can be supplied into the foreignmatter removing tank, whereby foreign matter can be effectively removed.

A washing solution for a photomask according to a twelfth aspect of thepresent invention contains H₂ gas dissolved water. Thus, foreign mattercan be effectively removed.

In a washing solution for a photomask according to a thirteenth aspectof the present invention, the H₂ gas dissolved water is alkalized. Thus,a removal ratio is further improved.

In a washing solution for a photomask according to a fourteenth aspectof the present invention, the H₂ gas dissolved water is alkalized withammonia.

Since the H₂ gas dissolved water is alkalized with ammonia, the washingeffect can be improved with even extremely low concentration of ammonia.

A method according to a fifteenth aspect of the present inventionrelates to a method of washing a halftone phase-shift photomask formedwith an MoSiON film. According to this method, foreign matter is washedout with H₂ gas dissolved water, whereby variations in the transmittanceof the MoSiON can be suppressed below a maximum allowable limit and thewashing efficiency can be improved.

The foregoing and other objects, features, aspects and advantages of thepresent invention will become more apparent from the following detaileddescription of the present invention when taken in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graph showing removal ratios for silica grains on a CrONfilm after treatment with various types of chemical solutions;

FIG. 2 is a conceptual diagram of an overflow tank provided with anultrasonic oscillator;

FIG. 3 is a conceptual diagram of a process for forming H₂ gas dissolvedwater;

FIG. 4 is a graph showing variations in the transmittance of an MoSiONfilm after alkali treatment;

FIG. 5 is a graph showing removal ratios for alumina grains on an MoSiONfilm after treatment with various types of chemical solutions;

FIG. 6 is a conceptual diagram of the flow of a photomask washingprocess;

FIG. 7 is a conceptual diagram of a photomask washing apparatus;

FIG. 8 is a conceptual diagram of a method of washing a photomasksubstrate horizontally rotating the photomask substrate;

FIG. 9 is a conceptual diagram of a method of washing a photomasksubstrate employing a line-type megasonic nozzle;

FIG. 10 is a graph showing the numbers of detected foreign matterremaining on a CrON film after resist removing treatment; and

FIG. 11 illustrates the flow of a conventional mask washing process.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiments of the present invention are now described with reference tothe drawings.

First Embodiment

With reference to a first embodiment of the present invention, a methodof effectively removing fine dust, metal, organic matter and the likeadhering to a surface of a photomask in fabrication steps is described.Silica (SiO₂) grains were deposited as foreign matter to the surface ofa photomask formed with a CrON film as a shading film. The photomask wasdipped in various types of chemical solutions in an overflow tank 301made of quartz shown in FIG. 2, and subjected to megasonic irradiationthrough an ultrasonic oscillator 302. FIG. 1 shows removal ratios forthe silica grains on the CrON film after treatment with the chemicalsolutions.

As shown in FIG. 1, an experiment was made with chemical solutions A(high purity water), B (diluted aqueous ammonia (pH 10)), C (aqueousammonia of 0.1% in concentration), D (H₂ gas dissolved water), E (H₂ gasdissolved water mixed with a small amount of aqueous ammonia so that thepH was about 10) and F (H₂ gas dissolved water mixed with 0.1% ofammonia) and foreign matter removal ratios were determined. The H₂ gasdissolved water is high purity water in which H₂ gas is dissolved, and amethod of forming the H₂ gas dissolved water is described later.

The H₂ gas dissolved water employed in this experiment was prepared byelectrolyzing high purity water so that H₂ gas formed on the cathodeside was dissolved in the high purity water, and the concentration ofthe H₂ gas was about 1.3 ppm. The removal ratio is expressed in theratio of the number of grains removed by the treatment to the number ofgrains present before the treatment.

As dearly understood from FIG. 1, the removal ratios with the highpurity water and the diluted aqueous ammonia (pH 10) were 0.1% and 30%respectively, and the silica grains employed as foreign matter werehardly removed. In the case of H₂ gas dissolved water, the silica grainswere removed in a removal ratio of about 30%. In the case of H₂ gasdissolved water mixed with an extremely small amount of aqueous ammoniaso that the hydrogen ion concentration (pH) was about 10, the removalratio was improved to about 65%. In the case of H₂ gas dissolved watermixed with about 1% of aqueous ammonia, the silica grains were removedwith a high removal ratio of 99%. In the case of the water in whichammonia of 0.1% in concentration was dissolved, the removal ratio was52% (see graph C).

Thus, when mega-ultrasonic waves treatment is carried out in high puritywater (H₂ gas dissolved water) in which H₂ gas is dissolved, particulateforeign matter adhering to the surface of the photomask can beeffectively removed. Further, it has been proved that removal efficiencyfor the foreign matter adhering to the surface of the photomask can beremarkably improved by employing H₂ gas dissolved water mixed with asmall amount of ammonia.

The concentration of ammonia used for the chemical solution havinghydrogen ion concentration (pH) of about 10 is about 0.003%, and thewashing effect of the H₂ gas dissolved water can be improved with suchlow concentration of ammonia. Thus, the amount of the chemical solutioncan be remarkably reduced as compared with the conventional washingmethod. As compared with a case of using a concentrated chemicalsolution, the amount of high purity water used for rinsing the photomaskafter the washing treatment can be remarkably reduced. Further, thewashing time can be reduced due to the improvement of the washingability, thereby saving energy such as electricity.

FIG. 3 shows a method of forming H₂ gas dissolved water. H₂ gas isdirectly supplied from a gas cylinder or generated by electrolyzingwater, and dissolved in high purity water in a gas dissolution unit. Thegas is dissolved by a method of supplying the gas and high purity waterinto a stirrer with a pump, generating a number of bubbles in the waterand stirring the same or a method of dissolving the gas in high puritywater through a gas permeation film. The hydrogen ion concentration canbe changed by adding a chemical solution such as diluted aqueous ammoniato the H₂ gas dissolved water formed by such a method.

Second Embodiment

With reference to a second embodiment of the present invention, awashing method optimum for removing foreign matter from a phase-shiftphotomask such as a halftone photomask is described.

A shading film for a halftone mask is formed by an MoSiON film. A glasssubstrate formed with such an MoSiON film of about 0.1 μm was dipped invarious types of washing solutions for two hours, to determinevariations (%) in the transmittance at a wavelength of 246 nm.

FIG. 4 illustrates the variations in the transmittance after washing. Anexperiment was made with washing solutions A (aqueous ammonia of 1%concentration), B (aqueous ammonia/aqueous hydrogen peroxide), C(aqueous ammonia of 5% concentration), D (aqueous ammonia of 10%concentration), E (H₂ gas dissolved water) and F (H₂ gas dissolved watermixed with a small amount of aqueous ammonia (pH 10)), as shown in FIG.4.

Through treatment with the aqueous ammonia/aqueous hydrogen peroxide (B)used in conventional photomask washing for removing foreign matter, thetransmittance was increased by about 1.04%. In the high purity water (C)having the ammonia concentration of 5% and the high purity water (A)having the ammonia concentration of 1%, the transmittance was increasedby 0.9% and 0.27% respectively. In the H₂ gas dissolved water (E) andthe H₂ gas dissolved water (F) of pH 10 mixed with a small amount ofaqueous ammonia, however, the transmittance was increased by only 0.02%and 0.1% respectively.

When the transmittance of an MoSiON film formed on the surface of aphotomask as a shading film varies, the shape and dimensions of a resistcircuit pattern transferred onto a wafer vary to finally deteriorate thecharacteristics of an LSI. Therefore, the transmittance of the MoSiONfilm is strictly managed. The conventional treatment with aqueousammonia/aqueous hydrogen peroxide cannot be employed for washing aphotomask formed with an MoSiON film, due to remarkable variation in thetransmittance. However, the fluctuation of the transmittance in the H₂gas dissolved water and the H₂ gas dissolved water of pH 10 mixed with asmall amount of ammonia shown in FIG. 4 is allowable.

FIG. 5 shows removal ratios for alumina (Al₂O₃) grains subjected tomegasonic irradiation in various types of solutions. The alumina (Al₂O₃)grains were deposited onto the MoSiON film as foreign matter.

The removal ratio was obtained by dividing the number of grains removedthrough megasonic irradiation by the number of grains present before thetreatment. An experiment was made with solutions A (high purity water),B (diluted aqueous ammonia of pH 10), C (H₂ gas dissolved water), D (H₂gas dissolved water of pH 10 mixed with a small amount of aqueousammonia), E (H₂ gas dissolved water having ammonia concentration of 1%)and F (aqueous ammonia/aqueous hydrogen peroxide), as shown in FIG. 5.

As a result, the following were proved: In the high purity water (A),the dilute aqueous ammonia (B) and the H₂ gas dissolved water (C), theremoval ratios were 5.0%, −0.2% and 0.0% respectively, and the aluminagrains were hardly removed. In the H₂ gas dissolved water mixed with asmall amount of aqueous ammonia (D), however, the alumina grains wereremoved with a removal ratio of 31.6%. In the catholyte of 1% ammoniaconcentration (E) prepared by further increasing the amount of aqueousammonia, the alumina grains were removed with a removal ratio of 39.6%.In the generally employed aqueous ammonia/aqueous hydrogen peroxide (F)effective for removing foreign matter, the removal ratio was 31%. Thus,it has been proved that the H₂ gas dissolved water (D) mixed with asmall amount of aqueous ammonia attains an effect of removing foreignmatter equivalent to that of the aqueous ammonia/aqueous hydrogenperoxide (F).

In other words, it has been proved from the results shown in FIGS. 4 and5 that a washing effect equivalent or superior to that of the prior artcan be attained without varying the transmittance of the MoSiON film bywashing out foreign matter with H₂ gas dissolved water mixed with asmall amount of ammonia of 0.003% concentration. If the ammoniaconcentration is not more than 1%, the variation in the transmittancecan be suppressed below the management criteria (e.g., 0.5%) whileimproving the washing efficiency by limiting the washing treatment to ashort time.

Third Embodiment

In the first and second embodiments, aqueous ammonia was added to H₂ gasdissolved water. In a third embodiment of the present invention, achemical solution rendered slightly alkaline by adding a small amount ofelectrolyte such as KOH in place of aqueous ammonia was employed. Asimilar effect can be attained also in this case.

Fourth Embodiment

The effects described with reference to the first and second embodimentscan be attained by dipping a photomask substrate in H₂ gas dissolvedwater or H₂ gas dissolved water mixed with a small amount of aqueousammonia introduced into a conventional overflow tank, as shown in FIG.2. The washing effect is further improved by applying ultrasonic waves.

Fifth Embodiment

The overall steps of washing a photomask are described with reference toa fifth embodiment of the present invention.

FIG. 6 illustrates the flow of a high-performance washing processaccording to the present invention. In a step 1, a photomask is washedwith a high-temperature mixed solution of sulfuric acid and aqueoushydrogen peroxide, in order to decompose organic matter such as resistand a solvent present on the surface of the photomask, improve thewettability of the surface and remove metal impurities. In a step 2, thephotomask is subjected to washing for removing sulfuric acid remainingon the surface of the photomask and foreign matter adhering thereto.

If a shading film formed on the washed photomask is a CrON film, thephotomask is subjected to mega-ultrasonic waves in H₂ gas dissolvedwater or H₂ gas dissolved water mixed with a small amount of ammonia asdescribed with reference to the first embodiment, for removingparticulate foreign matter adhering to the surface of the photomask.

The concentration of the ammonia used for the H₂ gas dissolved water isabout 0.003% when the pH of the H₂ gas dissolved water is 10. Thewashing effect can be improved with such extremely low concentration ofammonia, whereby the amount of the chemical solution (ammonia) can beremarkably reduced as compared with the conventional washing method. Ascompared with a case of using a concentrated chemical solution, further,the amount of high purity water used for rinsing the photomask after thechemical washing can be remarkably reduced.

In addition, the washing time for removing foreign matter can be reduceddue to the improved washing ability, and energy such as electricity canbe saved. The chemical solution remaining after removing organic matterand metal impurities with the mixed solution of sulfuric acid andaqueous hydrogen peroxide is rinsed out with H₂ gas dissolved watermixed with an electrolyte such as ammonia. Re-adhering of grainsfloating in the rinsing solution to the surface of the photomask duringrinsing is reduced as compared with the case of using high purity waterfor the rinsing, while the amount of the rinsing solution, the rinsingtime and energy such as electricity can be further saved.

If the photomask to be used is a halftone photomask and a shading filmformed thereon is an MoSiON film, foreign matter is removed by washingwith H₂ gas dissolved water mixed with a small amount of ammonia of0.003% concentration in the step 2, as shown in the second embodiment.When treating the photomask with such a chemical solution, a washingeffect equivalent or superior to that in the prior art can be attainedwithout varying the transmittance of the MoSiON film. If the ammoniaconcentration is not more than 1%, further, variation in thetransmittance can be suppressed below the management criteria (e.g.,0.5%) and the washing efficiency can be improved by limiting the washingto a short time. The effect can be further improved when mega-ultrasonicwaves are applied, as a matter course.

In a step 3, the washed photomask is dried to complete the process.

Through such a washing process, the efficiency for removing foreignmatter adhering to the photomask is improved as compared with the priorart, whereby the treatment time can be reduced and the amount of highpurity water and electrical energy can be saved. Further, the amount ofthe chemical solution used for washing can also be remarkably reduced.

Also when the shading film is an MoSiON film, the photomask can beeffectively washed without varying the transmittance thereof.

Sixth Embodiment

With reference to a sixth embodiment of the present invention, anapparatus for washing a photomask for implementing the photomask washingmethods according to the first to fifth embodiments is described.

FIG. 7 is a conceptual diagram showing a high-performance photomaskwashing apparatus according to the present invention. The washingapparatus is formed by an apparatus body 100 and a washing solutionsupply/control part 200 supplying a chemical solution or high puritywater to each tank arranged on the apparatus body 100 while setting andcontrolling the same to prescribed concentration and temperature. Theapparatus body 100 is formed by a sender unit 101, an acid tank 102, aforeign matter removing tank 103, a drying tank 104 and a receiver 105.The washing solution supply/control part 200 is formed by an acidpreparation tank 201, an alkali/detergent preparation tank 202, an H₂gas dissolved water forming unit 203, an IPA (isopropyl alcohol) unit204 and a control unit 205.

Operations of the apparatus are now described with reference to FIG. 7.

Photomasks are set on the sender unit 101 of the apparatus body 100. Atthis time, a plurality of photomasks are set on the sender unit 101 oneby one or at the same time. Each photomask set on the sender unit 101 isfed into the acid tank 102. In the acid tank 102, the photomask issubjected to acid treatment with sulfuric acid/aqueous hydrogen peroxideor the like supplied from the acid preparation tank 201. When thetreatment in the acid tank 102 is completed, the photomask is then fedinto the foreign matter removing tank 103. The foreign matter removingtank 103 is supplied with H₂ gas dissolved water formed in the H₂ gasdissolved water forming unit 203 and aqueous ammonia adjusted to aprescribed concentration in the alkali/detergent preparation tank 202 bythe control unit 205. In the foreign matter removing tank 103, thephotomask is subjected to mega-ultrasonic waves in the H₂ gas dissolvedwater, as described with reference to the first embodiment. Thus,particular foreign matter adhering to the surface of the photomask iseffectively removed. Further, the efficiency for removing foreign mattergrains adhering to the surface of the photomask can be remarkablyimproved by employing H₂ gas dissolved water mixed with a small amountof ammonia.

The concentration of the used ammonia in mixed with the H₂ gas dissolvedwater is about 0.003% when the pH of the H₂ gas dissolved water is 10.The washing effect can be improved with such extremely low concentrationof ammonia, whereby the amount of the chemical solution used (ammonia)can be remarkably reduced. As compared with the case of using aconcentrated chemical solution, further, the amount of high purity waterused for rinsing the photomask after the chemical washing can beremarkably reduced. In addition, the washing time for removing foreignmatter can be reduced due to the improved washing ability, and energysuch as electricity can be saved.

When each of the acid tank 102 and the foreign matter removing tank 103is formed as the overflow tank shown in FIG. 2, ultrasonics waves canalso be applied for further improving the washing effect. Further, theamounts of the high purity water and the chemical solution can be savedand the number of foreign matter contained in the chemical solution canbe controlled to a low level by overflowing and circulation-filteringthe chemical solution stored in each tank.

FIG. 8 shows an exemplary method of applying H₂ gas dissolved water oraqueous ammonia of low concentration onto the surface of the photomaskin each tank. As shown in FIG. 8, this method can be implemented byapplying H₂ gas dissolved water or H₂ gas dissolved water mixed with asmall amount of aqueous ammonia onto a surface of a horizontally rotatedphotomask substrate 40 from nozzles 41 fixed in a washing chamber (tank)or a nozzle fixed to a swinging arm 42. The nozzles 41 and the swingingarm 42 may be set in each of a plurality of tanks for dividing thewashing path in response to the type of the treated photomask.

A unit for horizontally rotating the photomask and applying a chemicalsolution containing H₂ gas dissolved water, high purity water or thelike onto the photomask from fixed nozzles or a nozzle fixed to aswingable arm can be set in the washing tank. With this unit, thephotomask can be washed by brush scrubbing. Further, H₂ gas dissolvedwater or H₂ gas dissolved water mixed with a small amount of aqueousammonia can be applied onto the mask from a swinging nozzle withapplication of mega-ultrasonic waves. Further, only high purity watersubjected to mega-ultrasonics waves can be applied onto the photomaskfrom such a mega-ultrasonic waves nozzle while applying aqueous ammonia,a mixed solution of aqueous ammonia and aqueous hydrogen peroxide, H₂gas dissolved water, H₂ gas dissolved water mixed with a small amount ofaqueous ammonia or the like from another nozzle for effectively removingforeign matter.

As a drying unit, a unit of steam drying with alcohol such as IPA, spindrying of rotating the photomask at a high speed in a horizontal stateor the like is connected. Referring to FIG. 7, an IPA steam drying unitis set on the apparatus.

When setting a spin drying unit, the IPA unit 204 is removed from thewashing solution supply/control part 200. The chemical solution used ineach unit is supplied from a chemical solution supply unit (not shown)independent of the apparatus body 100. A control unit such as asequencer for controlling the operations of the apparatus is set on thewashing solution supply/control part 200. The dried photomask is fedinto the receiver unit 105 and stored in a dedicated case or the like.

Seventh Embodiment

The effects of the first to fourth embodiments can be attained by usinggeneral line-type mega-ultrasonic waves nozzles 50 and rinsing aphotomask substrate 40 with megasonic irradiation in H₂ gas dissolvedwater or H₂ gas dissolved water mixed with a small amount of aqueousammonia, as shown in FIG. 9.

Eighth Embodiment

Foreign matter remaining on a CrON film after removing resist wasdetected. FIG. 10 shows the numbers of detected foreign matter. In thestep of removing the resist from a photomask, the resist was removed bywet treatment with a chemical solution. FIG. 10 shows the number offoreign matter remaining on the photomask rinsed with high purity waterand that of foreign matter remaining on the photomask rinsed with H₂ gasdissolved water in comparison with each other. The number of theremaining foreign matter was reduced to ¼ when the high purity water wasreplaced with the H₂ gas dissolved water. Thus, the number of remainingforeign matter can be reduced by employing H₂ gas dissolved water notonly in the washing step but also in the resist removing step. Further,a similar effect can be attained by treating the photomask in H₂ gasdissolved water mixed with ammonia.

Ninth Embodiment

The effects of the first to fourth embodiments can be attained not onlyin relation to a photomask substrate formed with a pattern but also inapplication to wet treatment of a photomask blank for forming aphotomask.

Although the present invention has been described and illustrated indetail, it is clearly understood that the same is by way of illustrationand example only and is not to be taken by way of limitation, the spiritand scope of the present invention being limited only by the terms ofthe appended claims.

What is claimed is:
 1. An apparatus for washing a photomask comprising:an acid tank for removing organic matter and metal impurities present onthe surface of a photomask with a first washing solution; a foreignmatter removing tank for removing foreign matter adhering to saidsurface of said photomask with a second washing solution containing H₂gas dissolved water; a drying tank for drying said photomask; firstwashing solution supply means supplying said first washing solution tosaid acid tank; first control means provided on said first washingsolution supply means for controlling the concentration and thetemperature of said first washing solution; second washing solutionsupply means supplying said second washing solution to said foreignmatter removing tank; and second control means provided on said secondwashing solution supply means for controlling the concentration and thetemperature of said second washing solution.
 2. The apparatus forwashing a photomask in accordance with claim 1, wherein said foreignmatter removing tank is provided with ultrasonics waves applicationmeans for supplying ultrasonic waves into said foreign matter removingtank.
 3. The apparatus for washing a photomask in accordance with claim1, wherein said acid tank is provided with ultrasonics waves applicationmeans for supplying ultrasonic waves into said acid tank.
 4. Theapparatus for washing a photomask in accordance with claim 1, furthercomprising aqueous ammonia supply means provided in said foreign matterremoving tank for supplying aqueous ammonia of prescribed concentrationinto said foreign matter removing tank.